MRI of the Lumbar Spine Michael Wilczynski, DO FAOCR Donald Kim, DO Diagnostic Radiology Department Chair Radiology Residency, St James Healthcare Franciscan St James Healthcare Abdominal Imaging Fellowship, UCSF Chicago, IL * Definition from Merriam Webster dictionary MRI sequences (truncated list) T1 flow sensitive gadolinium enhanced MR angiography MR venography fat suppressed CSF flow studies T2 miscellaneous fat suppressed MR cholangiopancreatography (MRCP) fluid attenuated MR spectroscopy susceptibility sensitive MR perfusion proton density functional MRI fat suppressed Tractography DTI diffusion weighted MR Elastography MR prostate MRI basics – Quick hits T1 T1-weighted images are generally considered to show the best anatomy Although they are not that sensitive to pathology They have the best signal-to-noise per-unit time of scanning On T1-weighted images: Tissues with short T1 times (like subcutaneous fat or fatty bone marrow) appear bright Tissues with long T1 times (like fluid, cotical bone) appear dark If “fat saturation” is used, fat will appear dark on a T1-weighted image. MRI basics – Quick hits T1 – Post contrast Often post contrast T1 sequences are also fat suppressed to make this easier to appreciate enhancement Enhancement = accumulation of contrast (mostly due to leaky blood vessels) Tumors Areas of inflammation Infection MRI basics – Quick hits T2 T2-weighted images are the most sensitive to pathology Tissues with short T2s appear dark tendons, ligaments, menisci, periosteum, cortical bone Tissues with long T2s are bright Since fluid has a long T2, joint effusions and muscle or bone marrow edema appear bright However, fat appears bright. In order to see subtle bone marrow edema, fatty bone marrow must be suppressed Another way to suppress fat is to use a technique called short T1 inversion recovery (STIR) MRI basics – Quick hits Identifying T1 vs T2 Easiest way to determine which pulse sequence was used is to look at the cerebrospinal fluid If the CSF is bright (high signal), it must be a T2-weighted image If the CSF is dark (low signal), it is a T1-weighted image MRI basics – T1 vs T2 T1: T2 Black (low intensity) Black (low intensity) Fluid (e.g. urine, CSF) White matter [Fat; if fat saturated image] Gray (intermediate intensity) Gray (intermediate intensity) Muscle Muscle Gray matter Gray matter White (High intensity) White (High intensity) Fat Fluid (e.g. urine, CSF) White matter [Fat; if NOT fat saturated image] MRI basics – CT vs MRI MR and CT are both competitive and complimentary CT MR Performs better in cases of trauma and Functions best as an elective outpatient emergent situations procedure Better bone detail Proper screening of patients, equipment, and personnel for Higher sensitivity for acute hemorrhage ferromagnetic materials, pacemakers, CT scanning is fast etc. is mandatory Imaging also requires more time LUMBAR SPINE Clinical Indications With its high contrast and spatial resolution and lack of ionizing radiation, MRI is considered by many to be the best imaging technique for the investigation of LBP Limitations Among patients without red flags (clinical signs and symptoms indicating serious underlying conditions), early imaging (vs conservative treatment without imaging) does not improve patient outcomes MRI is expensive High prevalence (64%) of abnormal findings among individuals without LBP This high prevalence makes it difficult, or possibly even perilous, to attribute a patient’s symptoms to certain imaging findings Approximately 70% of acute LBP patients can attribute their pain to spinal muscle strain or sprain Clinical Indications Indications for when to get an MRI scan include: After 4 to 6 weeks of leg pain, if the pain is severe enough to warrant surgery After 3 to 6 months of low back pain, if the pain is severe enough to warrant surgery If the back pain is accompanied by constitutional symptoms (such as loss of appetite, weight loss, fever, chills, shakes, or severe pain when at rest) that may indicate that the pain is due to a tumor or an infection For patients who may have lumbar spinal stenosis and are considering an epidural injection to alleviate painful symptoms For patients who have not done well after having back surgery, specifically if their pain symptoms do not get better after 4 to 6 weeks. ...or other “red flags” symptoms Contrast – with or without Clinical Contra-Indications Contraindications for undergoing an MRI scan for spine-related pain in the back, neck or leg include: Patients who have a heart pacemaker may not have an MRI scan Patients who have a metallic foreign body (metal sliver) in their eye, or who have an aneurysm clip in their brain, cannot have an MRI scan since the magnetic field may dislodge the metal Patients with severe claustrophobia may not be able to tolerate an MRI scan, although more open scanners are now available, and medical sedation is available to make the test easier to tolerate Patients who have had metallic devices placed in their back (such as pedicle screws or anterior interbody cages) can have an MRI scan, but the resolution of the scan is often severely hampered by the metal device and the spine is not well imaged. (Contrast reactions) Gadolinium Contrast Reactions Adverse Reactions Frequency of all acute adverse events ranges from 0.07% to 2.4% Mild (vast majority) coldness at the injection site, nausea with or without vomiting, headache, warmth or pain at the injection site, paresthesias, dizziness, and itching Severe/allergic reactions 0.004% to 0.7% Rash, hives, or urticaria are the most frequent of this group Bronchospasm Severe, life-threatening anaphylactoid or nonallergic anaphylactic reactions Nephrogenic systemic fibrosis (NSF) rare but serious systemic disease is characterized by fibrosis of the skin and other tissues throughout the body Exact etiology of NSF is unclear Most reported cases have been documented in patients with severe acute or chronic renal failure, Glomerular filtration rate (GFR) < 30. Extravasation of IV contrast Gadolinium Contrast Reactions Risk Factors 8 times higher risk in patients with a previous reaction to gadolinium-based contrast media Persons with asthma and various other allergies are also at greater risk If concern for contrast reaction, recommend standard premedication prep with steroid and antihistamine. Standard L-Spine Sequences T1-weighted Axial Sagittal T2-weighted Axial Sagittal STIR or T2 fat sat Sagittal L-spine search pattern A B C D E L-spine search pattern Alignment Bone Cord/Canal Discs Everything else L-spine search pattern Alignment anterior vertebral bodies posterior vertebral bodies facets posterior spinal canal line spinous processes L-spine search pattern Alignment Spondylolisthesis Etiology Trauma Degenerative Congenital Spondylolisthesis Mild (T1) Mod/Severe (T2) L-spine search pattern Bone Fractures Vertebral body compression Blastic / lytic lesions L-spine search pattern Bone / Bone Marrow Fractures Vertebral body compression Grading mild: 20-25% moderate: 25-40% severe: >40% Blastic / lytic lesions Thoracolumbar Injury Classification and Severity (TLICS) Scale Compression Fractures Mild/Mod Severe (T1) (T2) (T1) (STIR) Acute Chronic This MRI side view shows that the bone marrow Sagittal T1 W (a), T2 W (b) and STIR (c) MR indicated by the arrow has a whiter appearance images of spine show moderate/grade 2 indicating the bone fracture, with the signal change fracture in D12 (arrow) without any edema due to edema and swelling associated with the suggestive of chronic fracture fracture process. Normal Bone marrow 28-year-old man with 64-year-old woman with vague back pain. chronic low back pain. Sagittal T1-weighted spin- Central hyperintense echo image shows signal (arrows) is seen normal marrow signal within vague intensity of lumbar hypointense lesions vertebral bodies, which within L2 and L3 are slightly hyperintense vertebral bodies on this relative to adjacent sagittal T1-weighted intervertebral disks. White image, consistent with arrowheads depict bull’s eye sign of normal normal fat signal intensity hematopoietic marrow. in region of basivertebral Overall heterogeneous plexus. appearance of marrow is due to osteoporosis. Metastatic disease Progressive metastatic disease to bone at MRI. a. Baseline sagittal T1-weighted MR image of the lumbar spine with a typical normal bone marrow pattern (homogeneous high signal intensity). b. Three- month follow-up MR image shows appearance of multiple low signal areas corresponding to metastases ( arrows ). L-spine search pattern Cord/Canal Cord normally terminates at L1-2 Cord compression Canal hematoma Tumors Cord compression The spinal cord may be compressed by bone, hematoma, abscesses, tumors, or a ruptured or herniated disk. Symptoms can include back pain, abnormal sensations, muscle weakness, or impaired bladder and bowel control. Diagnosis based on symptoms and the results of a physical examination and/or magnetic resonance imaging. …look for cord edema/expansion • Cord compression is an emergency 70 year old male with vertebral body metastasis and intramedullary metastasis from renal cell carcinoma A.Pre-contrast sagittal T1wtd. MRI of the lumbar spine A. bony metastasis (yellow arrow) is seen involving the T12 vertebral body B.Post-contrast (C+) sagittal T1wtd. MRI A. yellow arrow points to the bony metastasis that enhances with contrast B. red arrow points to intramedullay location